1. Field of the Invention
The present invention relates to polynucleotides corresponding to the plsC gene and which encode 1-acyl-SN-glycerol-3-phosphate acyltransferase, methods of producing L-amino acids, and methods of screening for polynucleotides which encode proteins having 1-acyl-SN-glycerol-3-phosphate acyltransferase activity.
2. Discussion of the Background
Amino acids, particularly L-lysine and L-glutamate, are used in human medicine, in the pharmaceutical industry, in the food industry, and are used in particular in animal nutrition.
It is known that amino acids are produced by the fermentation of strains of coryneform bacteria, particularly Corynebacterium glutamicum. Due to the considerable importance of these amino acids, attempts are continuously being made to improve the production process. Process improvements can involve fermentation technology measures, such as stirring and supplying with oxygen for example, or can relate to the composition of the culture media, such as the sugar concentration during fermentation for example, or to work-up to give the desired form of product by ion exchange chromatography for example, or to the intrinsic production properties of the microorganism itself.
Methods of mutagenesis, selection and mutant selection are employed in order to improve the production properties of these microorganisms. In this manner, strains are obtained which are resistant to antimetabolites, such as the lysine analogon S-(2-aminoethyl)-cysteine for example, or which are auxotrophic for metabolites of regulatory importance, and which produce L-amino acids such as L-lysine or L-glutamate for example.
Moreover, for some years methods of recombinant DNA technology have been used to improve strains of Corynebacterium which produce amino acids. This has been achieved by amplifying individual amino acid biosynthesis genes and investigating the effect on amino acid production. Review articles on this topic, amongst other sources, are those by Kinoshita (xe2x80x9cGlutamic Acid Bacteriaxe2x80x9d, in: Biology of Industrial Microorganisms, Demain and Solomon (Eds.), Benjamin Cummings, London, UK, 1985, 115-142), Hilliger (BioTec 2, 40-44 (1991)), Eggeling (Amino Acids 6:261-272 (1994)), Jetten and Sinskey (Critical Reviews in Biotechnology 15, 73-103 (1995)) and Sahm et al. (Annals of the New York Academy of Science 782, 25-39 (1996)).
However, there remains a critical need for improved methods of producing L-amino acids and thus for the provision of strains of bacteria producing higher amounts of L-amino acids. On a commercial or industrial scale even small improvements in the yield of L-amino acids, or the efficiency of their production, are economically significant. Prior to the present invention, it was not recognized that enhancement or over-expression of the plsC gene, encoding 1-acyl-SN-glycerol-3-phosphate acyltransferase, would improve L-amino acid yields.
One object of the present invention, is providing a new process adjuvant for improving the fermentative production of L-amino acids, particularly L-lysine and L-glutamate. Such process adjuvants include enhanced bacteria, preferably enhanced coryneform bacteria which express high amounts of 1-acyl-SN-glycerol-3-phosphate acyltransferase which is encoded by the plsC gene.
Thus, another object of the present invention is providing such an enhanced bacterium, which expresses an enhanced amount of 1-acyl-SN-glycerol-3-phosphate acyltransferase or gene products of the plsC gene.
Another object of the present invention is providing a bacterium, preferably a coryneform bacterium, which expresses a polypeptide that has an enhanced 1-acyl-SN-glycerol-3-phosphate acyltransferase.
Another object of the invention is to provide a nucleotide sequence encoding a polypeptide which has 1-acyl-SN-glycerol-3-phosphate acyltransferase sequence. One embodiment of such a sequence is the nucleotide sequence of SEQ ID NO: 1.
A further object of the invention is a method of making 1-acyl-SN-glycerol-3-phosphate acyltransferase or an isolated polypeptide having a 1-acyl-SN-glycerol-3-phosphate acyltransferase activity, as well as use of such isolated polypeptides in the production of amino acids. One embodiment of such a polypeptide is the polypeptide having the amino acid sequence of SEQ ID NO: 2.
Other objects of the invention include methods of detecting nucleic acid sequences homologous to SEQ ID NO: 1, particularly nucleic acid sequences encoding polypeptides that have 1-acyl-SN-glycerol-3-phosphate acyltransferase activity, and methods of making nucleic acids encoding such polypeptides.
The above objects highlight certain aspects of the invention. Additional objects, aspects and embodiments of the invention are found in the following detailed description of the invention.